When nonhuman primates are confined to cages, boredom, stress and other negative psychological reactions can result. Such consequences of confinement tend to produce slanted experimental results, both in endocrine tests and, more clearly, in behavioral tests. Such results are noticeable with rhesus monkeys, for example, which tend to be social animals but which, moreover, exhibit aggressive tendencies. In many cases, caged confinement tends to exacerbate the manifestation of abnormal psychological reactions.
Several investigators have attempted to determine various alterations which may be made in a single cage environment of singly-housed laboratory primates in order to enhance the "psychological well-being" of these animals, where "psychological well-being" is defined predominantly by an absence of behavioral pathology of the nonhuman primates in a laboratory environment.
Such prior art attempts to enhance the "psychological well-being" of the animals include provision of control for the animals over the physical environment thereof, disclosed by Spinnelli and Markowitz in 1985; exercise cages, described by Tolan et al. in 1980; provision of nylon balls, described by Renquist and Judge in 1985.
However, none of the above attempts provides environmental alterations which are easily implemented and which induce the animal to perform natural behaviors, i.e., behavior patterns occurring in noncaged animals, which require low maintenance, are cost effective and which can be provided for a large number of animals. Nor do the suggested alterations provide freedom from interference with accessability of the animals for participation in research, without harming the animal or placing the caretaking staff at risk.
Also known in the prior art are devices for relieving physical distress of animals, such as a cat scratching device disclosed in U.S. Pat. No. 3,482,548, which may be made available to felines to replace a cat scratching post or structure, without undue bulkiness in the result. However, such scratching posts provide relief for physical discomfort. That is, the feline animal requires a scratching post (or the like) for physical relief. The art does not disclose method or apparatus for relieving psychological stress.